SIMULATION OF LEDGEWISE GROWTH KINETICS OF PROEUTECTIOD FERRITE UNDER INTERFACIAL REACTION--DIFFUSION MIXED CONTROL MODEL

The effect of Cr addition on the transformation and the cyclic deformation characteristics in 550℃annealed Ti-50.8Ni shape memory alloy(SMA) were investigated by differential scanning calorimetry(DSC) and tensile test.The B2→R→M/M→B2 type reversiable transformation occurred in Ti-50.8Ni alloy upon cooling/heating.After the addition of 0.3%Cr in Ti-50.8Ni alloy the transformation type for Ti-50.8Ni-0.3Cr alloy was B2→R→M/M→R→B2,and the transformation temperatures decreased significantly.At room temperature,the phase composition was parent phase B2 for both Ti-50.8Ni and Ti-50.8Ni-0.3Cr alloys,while the former showed shape memory effect;the latter showed superelasticity.With increasing cyclic deformation number n,Ti-50.8Ni alloy evolved from shape memory effect to linear superelasticity,and its stress inducing martensitic critical stress and the accumulation residual strain increased rapidly;while Ti-50.8Ni-0.3Cr alloy evolved from incomplete superelastic to complete superelastic,and the stress-train curve shape was stable.With increasing n,the superelastic residual straine_r decreased and the superelastic strain recovery ratioη_s of Ti-50.8Ni alloy increased,while thee_r andη_s in Ti-50.8Ni-0.3Cr alloy kept at lower and higher values,respectively. The superelastic of Ti-50.8-0.3Cr alloy was stable.